Aqueous slurries, which basically comprise an aqueous medium and particulates are commonly used in the oil and gas industry to transport particulates through a pipe or tube, either on ground, or from the surface to a subterranean formation or from a subterranean formation to the surface. The most commonly used particulates include sand, ceramic particulates, glass spheres, bauxite (aluminum oxide) particulates, resin coated particulates and synthetic particulates (with sand being the most commonly used particulate). The particulates normally range in size from about 10 to about 100 U.S. mesh, which is from about 150 to 2000 μm in diameter, and have significantly higher density than water. For example, the density of sand is typically about 2.6 g/cm3 while the density of water is 1 g/cm3. Sand is by far the most commonly used particulate.
Aqueous slurries are widely used in oil and gas industry including drilling and hydraulic fracturing operations. To make relatively stable slurry, the particulates must be suspended in a liquid medium for a lengthy period of time at static and/or dynamic conditions, and therefore the viscosity or viscoelasticity of the liquid medium must be sufficiently high to be able to suspend the particulates. The most commonly used method for increasing viscosity or viscoelasticity of an aqueous liquid is by adding a viscosifier, for example, a natural or synthetic polymer or a viscoelastic surfactant to the liquid medium.
Hydraulic fracturing is a technology used to enhance oil and gas production from a subterranean formation. During the operation, a fracturing fluid is injected through a wellbore into a subterranean formation at a pressure sufficient to initiate fractures in the formation. Frequently, the fracturing fluid comprises particulates, commonly known as proppants, suspended in the fluid and transported as a slurry into the fractures. At the last stage of the fracturing operation, fracturing fluid is flowed back to the surface leaving proppants in the fractures forming proppant packs to prevent fractures from closing after pressure is released (i.e., the particulates “prop” open the factures). The proppant packs provide highly conductive channels for hydrocarbon to effectively seep through the subterranean formation. Proppants, including sands, ceramic particulates, bauxite particulates, glass spheres, resin coated sands, synthetic particulates and the like, are known in the industry. Among them sands are by far the most commonly used proppants. As noted above, the proppants normally range in size from about 10 to 100 U.S. mesh, which is about 150 to 2000 μm in diameter.
Fracturing fluids in common use include various aqueous-based and non-aqueous based (e.g., hydrocarbon-based) fluids. Due to their low cost and high versatility, aqueous-based fluids are preferred and most commonly used. To better transport particulates, water-soluble viscosifiers, such as polymers (i.e., linear or cross-linked polymers) or viscoelastic surfactants are commonly added to increase fluid viscosity. For example, a polymer, such as guar gum or its derivatives, is added into an aqueous liquid wherein the physical entanglement of polymer chains increases the fluid viscosity and thus its suspension capability. To further enhance fluid viscosity, it is common to chemically cross-link polymer chains by certain chemical compounds forming cross-linked gel. Guar gum cross-linked by borates is one of the examples. Compared to the cross-linked fluid, linear gels, i.e., fluids containing sufficient amount of polymers without cross-linking, cause less formation damage and are more cost-effective, but have relatively poor suspension capability. As well, viscoelastic surfactants cause less damage, but are much more expensive. In recent years, slick water, i.e., water containing very small amounts of friction reducing agent (usually in the range from about 0.015% to 0.06% of the fluid), is widely used as a fracturing fluid, especially for fracturing shale formations. Various water-soluble polymers including guar gum and its derivatives and polyacylamide and its derivatives have been used as friction reducing agents. Polyacrylamides, including different polyacrylamides copolymers, are most widely used as friction reducing agents in hydraulic fracturing operations.
As noted above, the last stage of a fracturing treatment involves the flowing of the fracturing fluid back to the surface while the proppants are left in the fractures. It is not unusual for a significant amount of proppant to be carried out of the fractures and into the wellbore along with the fluids being flowed back out the well. This process is known as proppant flowback. Proppant flowback is highly undesirable because it not only reduces the amount of proppants remaining in the fractures resulting in less conductive channels, but also causes significant operational difficulties. This problem has long plagued the petroleum industry because of its adverse effect on well productivity and equipment. Numerous methods have been attempted in an effort to find a solution to the problem of proppant flowback. The commonly used method is the use of so-called “resin-coated proppants”. The outer surfaces of the resin-coated proppants have an adherent resin coating so that the proppant grains are bonded to each other under suitable conditions forming a permeable barrier and reducing the proppant flowback (i.e., the proppant grains become tacky and stick together to reduce proppant flowback). For example, see U.S. Pat. Nos. 4,585,064 and 6,047,772.
There are significant limitations to the use of resin coated proppants, including that the method is expensive and operationally challenging. For example, resin-coated proppants are much more expensive than normal sands, especially considering that a fracturing treatment usually employs tons of proppants in a single well. Normally, when the formation temperature is below 60° C., activators are required to make the resin-coated proppants bind together. This increases the cost.
There is thus a need for a composition and method for making slurry which can form a stable proppant pack and resist/reduce proppant flowback, while at the same time is more cost effective and/or operationally simple.
When drilling subterranean formations for oil and gas, aqueous-based drilling fluids are normally used. During the drilling process large amounts of particulates, called cuttings are generated. Cuttings have different sizes ranging from fines to pebbles. The drilling fluid is circulated through the wellbore to make slurry with the cuttings in situ and transports them out of wellbore. In most cases, polymers as well as clays are added to the drilling fluids to increase their viscosity/viscoelasticity in order to transport the cuttings efficiently. However, polymers, as well as clay fines, can easily penetrate into pores or thin fractures in a formation and significantly reduce formation permeability, especially at near wellbore. Reduced formation permeability impedes oil and/or gas production. Therefore it is highly desirable to have a drilling fluid that can make stable slurry in situ with the cuttings and transport them out of the wellbore, while causing less formation damage.
In oil sand operation massive amount of sands are left after oil is stripped off sand surface. Finding a more cost effective way to transport sands efficiently over distance through pipelines has long been required in the industry. Thus, a composition and a method for making stable and highly fluid sand slurries at low cost would be quite useful.
U.S. Pat. Nos. 7,723,274 and 8,105,986 teach a different way of enhancing the transporting capability of a slurry. Instead of focusing on improving fluid rheology, the patents teach enhancing the transporting capability of a slurry by rendering the particulate surfaces sufficiently hydrophobic to attach gas bubbles to particulate surfaces, and thus, buoying the particulates up. Consequently, particulates can be transported into the formation effectively without requiring addition of viscosifiers to the fluid. Different hydrophobising agents, including silicone compounds or hydrocarbon amines, are disclosed in U.S. Pat. Nos. 7,723,274 and 8,105,986.
In this application, we disclose an aqueous slurry composition, including methods of making and using such compositions, that is intended to address some of the deficiencies and problems with known slurry compositions (as discussed above). This aqueous slurry composition comprises an aqueous liquid, particulates and an amine functionalized hydrophobic polymer. This composition can be used in different operations, especially oil field operations, to efficiently transport particulates through a pipe or tube.